Cathodes for electron tubes



United States Patent 3,070,550 CATHQDES FOR ELECTRON TUBES Saburo Aoiand Noboru Murata, Tokyo, Japan, assignors to Oki Electric IndustryCompany, Ltd., Tokyo, Japan,

a corporation of Japan No Drawing. Filed Feb. 17, 1960, Ser. No. 9,182Claims priority, application Japan Feb. 25, 1959 1 Claim. (Cl. 252-621)This invention relates to cathodes for electron tubes which have a highefficiency of electron emission at compartively low temperature.

It is an object of the invention to provide cathodes for electron tubeswhich can emit suificient electrons without raising the heatingtemperature excessively.

It is another object of the invention to provide an improved cathode forelectron tubes which will not become deformed and will not spatterelectrodes surrounding the cathode.

It is a further object of the invention to provide a low melting pointoxide mixture for cathodes to reduce the temperature for activation invacuum in the manufacturing process of cathodes.

In conventional cathodes for electron tubes which consist of porousmetals containing oxide mixtures of two or more ingredients such abarium oxide, aluminum oxide, calcium oxide, magnesium oxide andstrontium oxide, the melting points of the oxide mixtures are generallyabove 1300 C. and as high as 1700 C. Therefore, an excessively hightemperature is required for impregnation, which makes the manufacturingof cathodes difiicult. Furthermore, since the efficiency of electronemission at 1000 C. is inferior, the heating temperature for suchcathodes must be raised to at least 1100 C. in order to obtainsufiicient electron emission. Consequently, the life of heatingfilaments for cathodes is shortened, the cathodes deform more readily,and surrounding electrodes surrounding the cathodes, are spattered bymaterial emitted by the cathode.

According to this invention, oxide mixtures of barium oxide, berylliumoxide and calcium oxide as shown in the following table are melted in ahydrogen furnace, coagulated, crushed and then impregnated into tungstenor other heat resisting porous metals in vacuum or at- "ice mospheres ofhydrogen, argon, etc. at such melting temperatures as shown in thetable:

As seen on the above table, the melting temperatures are lower thanthose of conventional oxide mixtures and temperatures for activation invacuum may be limited so as not to exceed 1030 C., which greatlyfacilitates the manufacturing of cathodes. The cathodes made inaccordance with the present invention will emit sufficient electrons asshown in the table. Moreover, in these cathodes the life of heatingfilaments is materially extended, the cathode-supporting metals will notdeform, and the electrodes surrounding the cathode will not bespattered. Therefore, the cathodes according to this invention aresuperior to known cathodes when used for electron tubes as they affordlong-life and high reliability to the tubes. These advantages areimportant in electron tubes generally and are particularly important inhigh power tubes such as microwave magnetrons and the like. Forinstance, the cathode impregnated with the mixture of 2 mols of bariumoxide, 1 mol of beryllium oxide and 1 mol of calcium oxide emit anelectron emission of 9.6 amperes per sq. cm. and afiords stableoperation during continuous operation of 1,500 hours or more.

What is claimed is:

Cathodes for electron tubes comprising heat-resisting porous metalsimpregnated with oxide mixtures of barium oxide, beryllium oxide andcalcium oxide in mixture proportions of 2 to 3 mols, 1 to 2 mols and V2to 1 mol respectively.

References Cited in the file of this patent UNITED STATES PATENTS2,902,621 Winter Sept. 1, 1959

